Animal Model Core B will provide all mice used in Projects 1, 2 and 3, i.e., it will be responsible for ordering mice, performing the various manipulations required to induce experimental colitis, maintaining a barrier facility, performing routine surveys to ensure absence of pathogens in the colony. And assist in harvesting tissues from such mice. Centralization of these functions in an Animal Model Core provides uniformity and quality control of mice being studied in the various projects, reduces cost, and should help conserve numbers of mice required by ensuring their optimal use in the projects. A second aim of the Animal Model Core is that of a centralized pathologic analyses which will be performed by Dr. Audrey Lazenby, an expert GI pathologist. Tissue sections from the various projects are coded prior to interpretation and quantitative scoring. This facilitates interactions among the projects and also the comparison of results between them. A third purpose of the Animal Model Core, which is new since the last submission, is to provide genetically modified transgenic and knockout mouse strains for use in experiments in the various projects. Such genetically altered strains are powerful analytic tools for defining the role of specific gene products in complex biologic systems that are becoming the "reagents" that allow fundamental questions to be experimentally addressed that had been previously unapproachable. Mice with induced mutations frequently have to be bred onto other background strains for optimal study, which requires screening of individual animals in each generation of identification of one or more target genetic elements. Approximately 30 mutant or genetically engineered strains are currently maintained in the Core. Dr. Charles Elson will serve as Director and Dr. Casey Weaver will serve as Co-Director of this Core. Mice are housed under barrier conditions in two locations, the 8th floor of the Lyons Harrison Research Building and the Animal Facility in the Wallace Tumor Institute. Dr. J. Russell Lindsay and Dr. Carl Pinkert from the Department of Comparative Medicine will serve as Consultants. An Oversight Committee consisting of the PI of each project with Dr. Lindsay and Dr. Pinkert will oversee the usage and function of the Core.